Then I would seriously be questioning the apparent support you are receiving.
And the fact you are still are using words like normal, narrasisst etc proves it.
No it isnt normal and any one who actually has a proper understanding of child development, impact of attachment along with the overlay of blended families would.
What she did isnt unforgivable. And I would seriously caution your mindset, because currently you still have small children who for the most part are still fully influenced and controlled by you.
In 10 years time that wont be the case. They will be primarily influenced by the peers. Which if they have a fairly stable and secure attachment type isnt to high risk.
How ever, throw in a few adverse situations and that can all change. Bullying, social media impact, poor self esteem. The list is fucking endless.
Then you could be facing a teen who hates the sight of you, experiments with drink or drugs, negative sexual experiences. And now the wheels have come all the way.
Zero control, poor emotional regulation, anger. And you could well end up sitting exactly were you are now.
Of course anger comes with dealing with teens with issues. But that anger becomes toxic and damaging to the child when it loses emotional maturity and regulation and compassion. With a dose of empathy.
Which you dont have.
Teens dont turn around and learn without a strong support base to do it. And plenty do. The world is full of perfectly functioning, happy, productive adults who went through hell as teens.